Expression of a Crry/p65 is reduced in acute lung injury induced by extracellular histones

Acute lung injury (ALI) occurs in patients with severe sepsis and has a mortality rate of 40%–60%. Severe sepsis promotes the release of histones from dying cells, which can induce platelet aggregation, activate coagulation and cause endothelial cell (EC) death. We previously reported that the expression of membrane complement receptor type 1‐related gene Y (Crry)/p65, which plays a principal role in defence against abnormal activation of complement in the blood, is reduced in response to peritoneal mesothelial cell injury, and we hence hypothesized that a similar mechanism occurs in pulmonary ECs. In this study, we examined the role of Crry/p65 in histone‐mediated ALI using an experimental animal model. In ALI model mice, exposure to extracellular histones induces lung injury and results in a decrease in Crry/p65 expression. The levels of lactic acid dehydrogenase (LDH), a marker of cell damage, were significantly increased in the serum of ALI model compared with vehicle mice. The significant inverse correlation between the expression of Crry/p65 and LDH levels in plasma revealed an association between Crry/p65 expression and cell damage. The levels of complement component 3a (C3a) were also significantly increased in the serum of the ALI model compared with vehicle mice. Notably, a C3a receptor antagonist ameliorated lung injury induced by histones. We hypothesize that extracellular histones induce complement activation via down‐regulation of Crry/p65 and that C3a might serve as a therapeutic target for the treatment of ALI.

Blockade of C3a/C3aR axis alleviates severe acute pancreatitis-induced intestinal barrier injury

Severe acute pancreatitis (SAP) contributes to multiple organ dysfunction and intestine is one of the most susceptible targets. This study aims to explore the role of C3a/C3aR axis in SAP-induced intestinal barrier injury. Adult male Sprague Dawley rats were randomly divided into control, SAP, C3aRA (0.06 mg/kg) and C3aRA (0.12 mg/kg) groups. SAP rat models were established by retrograde injection of 3.5% sodium taurocholate solutions into pancreatic ducts. Histopathological changes and dysfunction in pancreatitis and intestine were measured by hematoxylin and eosin (H&E) staining and detection of amylase (AMY), lipase (LIPA), endotoxins and diamine oxidase (DAO) levels in serum. Cell apoptosis was evaluated by TUNEL assay and western blot analysis. In addition, the expressions of caudin-1, caudin-2, occludin and ZO-1 were detected by western blot assay and immunohistochemical staining. Inflammatory cytokines and oxidative stress levels in SAP rats were determined. The C3a/C3aR expression was increased in pancreatic and intestinal tissues of successfully established SAP rat models. C3a receptor antagonist (C3aRA) alleviated pancreatic and intestinal pathological lesions and dysfunction induced by SAP. C3aRA inhibited cell apoptosis and promoted the expressions of caudin-1, caudin-2, occludin and ZO-1 in intestinal tissues. Moreover, C3aRA repressed inflammatory cytokines by reduction of TNF-α, IL-1β, IL-6 and MCP-1 levels, and ameliorated oxidative stress through regulation of ROS, MPO and SOD activity in rats with SAP-induced intestinal barrier injury. Our findings suggested that inhibition of C3a/C3aR axis diminished pancreatic damage and SAP-induced intestinal barrier injury in vivo, which may provide a new therapeutic strategy for SAP-induced intestinal injury.

The Role of Complement C3a Receptor in Stroke

The complement system is a key regulator of the innate immune response against diseased tissue that functions across multiple organ systems. Dysregulation of complement contributes to the pathogenesis of a number of neurological diseases including stroke. The C3a anaphylatoxin, via its cognate C3a receptor (C3aR), mediates inflammation by promoting breakdown of the blood-brain barrier and the massive infiltration of leukocytes into ischemic brain in experimental stroke models. Studies utilizing complement deficient mice as well as pharmacologic C3aR antagonists have shown a reduction in tissue injury and mortality in murine stroke models. The development of tissue-specific C3aR knockout mice and more specific C3aR antagonists is warranted to facilitate our understanding of the role of the C3aR in brain ischemia with the ultimate goal of clinical translation of therapies targeting C3aR in stroke patients.

Complement C3a receptor antagonist attenuates tau hyperphosphorylation via glycogen synthase kinase 3β signaling pathways

Neurofibrillary tangles aggregated from hyperphosphorylated tau protein are the main pathological feature of Alzheimer's disease (AD). Complement C3 (or C3a) is the core component of the complement system and is associated with AD pathological processes. However, it remains unclear whether C3a or the C3a receptor has any effect on tau phosphorylation. In this study, we found that exposure of SH-SY5Y cells to okadaic acid (OA) decreased cell viabilities and induced tau hyperphosphorylation. These effects were alleviated by C3a receptor antagonist SB290157 and were further validated by C3a receptor siRNA in OA-treated SH-SY5Y cells. In addition, our results demonstrated that SB290157 markedly inhibited the activities of glycogen synthase kinase 3β (GSK3β), but had no effect on protein phosphatase 2A C subunit (PP2Ac) and cyclin-dependent kinases 5 (CDK5). Our findings here indicate the unique role of the C3a receptor in regulating tau phosphorylation via GSK3β signaling pathways and suggest that the C3a receptor may be a viable target for treating AD.